1. Technical Field
Aspects of the present invention relate to a mass flow controller that controls the flow rate of a fluid, such as gas and liquid.
2. Related Art
In a related art semiconductor manufacturing apparatus to which various kinds of gas used for manufacturing a semiconductor are supplied, a mass flow controller is provided for each gas supply channel to adjust the flow rate of the gas. A related art pressure regulator is connected in series to each mass flow controller so as to prevent an extreme change in pressure in the channel to which the mass flow controller is attached, thereby facilitating flow rate control.
A related art flow rate control method for the mass flow controller is PID (proportional integral derivative) control. For example, a related art feedback control is based on a variation of the related art PID control disclosed in Japanese Laid-Open Patent Application No. 2004-280689 (hereafter “Patent Document 1”). According to the related art method disclosed in the Patent Document 1, the feedback control value is calculated by performing a PID calculation on the deviation, and multiplying the calculation result by a function whose value increases as the flow rate setting value decreases.
In a recent related art system, a regulator is provided only for a fluid supply source, such as a cylinder, rather than for each supply channel; however, the mass flow controller is provided for each supply channel.
This related art system configuration has at least the following disadvantage. If one of the supply channels is suddenly closed, or the flow rate of one of the mass flow controllers is substantially changed, the resulting pressure change affects the other supply channels or mass flow controllers (this is referred to as crosstalk). As a result the related art control method, which is based on the assumption that the pressure regulator controls the pressure change, may not be able to achieve adequate flow rate control.
More specifically, if the related art control method disclosed in the Patent Document 1 is used, and if the pressure on the primary side (the pressure on the upstream side of the mass flow controller) changes beyond a certain level, the flow rate excessively responds to the change and changes beyond a prescribed level.
As higher speed and precision are required in the related art control of the flow rate of the raw material gas or the like used in semiconductor processes, the speed of following the change of the flow rate setting value (the speed of response) cannot be sacrificed to suppress the above-described related art excessive response.